Propellers for high speed aircraft turn at low rotative speeds in order that the tip velocity will be effectively subsonic to avoid large performance losses due to compressibility effects and, when driven by turboshaft engines, usually require two stages of reduction gears to reduce the shaft speed from the high turboshaft speed to the slow propeller speed. These propellers customarily have three or four blades and, when compared to jet and turbofan engines, must be large in diameter to absorb the engine power. The structural requirement for thick airfoils with their low critical Mach number restrict the maximum aircraft operating speeds below those of turbofan powered aircraft. The need for low tip speeds for relatively high speed flight requires a slow shaft speed which can generally be obtained only with a two stage reduction gear which, because of the low speeds, must be relatively heavy. This heavy two-stage reduction gear severely increases the power plant weight and space requirements together with loss of efficiency in the power train. The large diameter propeller and attendant gear train pose installation problems in high speed aircraft and result in high gross weight of the propulsion system and weight penalties to the airframe.